Re: [PATCH 4/4] [x86] perf: fix accidentally ack'ing a second event on intel perf counter

[Peter Zijlstra <peterz@infradead.org>]

On Thu, 2010-09-02 at 16:39 +0200, Stephane Eranian wrote:
> I managed to reproduce on core i7 860 (without patch4).
> Looking at the code again, I am dubious you ever execute
> the retry goto. If the PMU is disabled and you've just
> cleared the OVF_STAT, then I don't see where the new
> overflows would come from. But that's a separate problem.
> 
> One thing I did is to compare status obtained via OVFL_STATUS
> with one that I build manually by inspecting each individual
> counter. The two returned bitmasks should always be identical
> (with PEBS disabled).  When I got the spurious NMI, it did not
> trip my status validation. So the OVFL_STATUS is valid.
> 
> I found something else that looked fishy. I am experimenting
> with it. I will report back. 

One thing we still need to do is on init detect if the BIOS is using one
of the PMCs and simply disable all of perf and print a nice big message
to the user to request a new BIOS from their vendor.